Quinones carbons

The quinone methide carbon of 71 is also the terminal carbon of an extended enol, and therefore reacts as both a nucleophile and electrophile (Scheme 32). This carbon shows a higher relative reactivity with electrophiles compared with nucleophiles than is observed for the corresponding terminal quinone carbon of mitomycins (Scheme 30A).73 Furthermore, the addition of nucleophiles to 71 is readily reversible, but the nucleophile adduct can be trapped by reoxidation to... 

NMR Spectra of Unreacted Samples. Quantitative liquid phase NMR spectra of the unreacted samples are shown in Figure 2. Peak areas of the spectra are listed in Table I together with elemental analyses. Characteristically, the humic acid has a greater aromatic carbon and lesser carboxylic acid carbon content than the fulvic acid. The naturally occurring nitrogen contents are 2.68% and 4.18% for the fulvic and humic acids, respectively. Overlap of functional groups which may serve as substrate sites for nucleophilic addition by aniline occurs within the major peak areas of the spectra. Quinone carbons (190 to 178 ppm) overlap with ketone carbons from 220 to 189 ppm, amides and esters (174 to 164 ppm) overlap with... 

The reductive half-reaction of methylamine dehydrogenase is shown in Scheme 10. The methylamine substrate initiates a nucleophilic attack on the quinone carbon at the C6 position of the TTQ cofactor displacing the oxygen to form a substrate-TTQ Schiff base adduct (29). The reactivity of the C6 position was demonstrated by covalent adduct formation at this position by hydrazines which are inactivators of methylamine dehydrogenase. Deprotonation of the substrate-derived carbon of 29 by an active-site amino acid residue results in reduction of the cofactor and yields an intermediate in which the Schiff base is now between the nitrogen and substrate-derived carbon (30). Hydrolysis of 30 releases the formaldehyde product and yields the aminoquinol form of the cofactor with the substrate-derived amino group still covalently bound (31). 

Kende, a. S., and P. C. Naegely Total Synthesis of the Streptonigrin Quinone Carbon Framework. Tetrahedron Letters 4775 (1978). 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

This addition is general, extending to nitrogen, oxygen, carbon, and sulfur nucleophiles. This reactivity of the quinone methide (23) is appHed in the synthesis of a variety of stabili2ers for plastics. The presence of two tert-huty groups ortho to the hydroxyl group, is the stmctural feature responsible for the antioxidant activity that these molecules exhibit (see Antioxidants). 

The mechanism of this reaction has been studied by several groups [133,174-177]. The consensus is that interaction of ester with the phenolic resole leads to a quinone methide at relatively low temperature. The quinone methide then reacts rapidly leading to cure. Scheme 11 shows the mechanism that we believe is operative. This mechanism is also supported by the work of Lemon, Murray, and Conner. It is challenged by Pizzi et al. Murray has made the most complete study available in the literature [133]. Ester accelerators include cyclic esters (such as y-butyrolactone and propylene carbonate), aliphatic esters (especially methyl formate and triacetin), aromatic esters (phthalates) and phenolic-resin esters [178]. Carbamates give analogous results but may raise toxicity concerns not usually seen with esters. 

The ready reversibility of this reaction is essential to the role that quinones play in cellular respiration, the process by which an organism uses molecular- oxygen to convert its food to carbon dioxide, water, and energy. Electrons are not transfened directly from the substrate molecule to oxygen but instead are transfened by way of an electron transport chain involving a succession of oxidation-reduction reactions. A key component of this electron transport chain is the substance known as ubiquinone, or coenzyme Q ... 

At least two pathways have been proposed for the Nenitzescu reaction. The mechanism outlined below is generally accepted." Illustrated here is the indolization of the 1,4-benzoquinone (4) with ethyl 3-aminocrotonate (5). The mechanism consists of four stages (I) Michael addition of the carbon terminal of the enamine 5 to quinone 4 (II) Oxidation of the resulting hydroquinone 10 to the quinone 11 either by the starting quinone 4 or the quinonimmonium intermediate 13, which is generated at a later stage (HI) Cyclization of the quinone adduct 11, if in the cw-configuration, to the carbinolamine 12 or quinonimmonium intermediate 13 (IV) Reduction of the intermediates 12 or 13 to the 5-hydroxyindole 6 by the initial hydroquinone adduct 7 (or 8, 9,10). 

The more interesting situation arises in quinones which possess two dissimilar substituents. The site of initial carbon-to-carbon condensation is explicable in terms of the relative electronic effects. Thus condensation of 2-chloro-5-methylbenzoquinone (19) with t-butyl 3-aminocrotonate (20) in hot acetic acid furnished the 4-chloro-7-methylindole (21) in 51% yield. ... 

Oxy-aldehyd, n, hydroxy aldehyde, -ammo-niak, n, oxyammonia (hydroxylamine), -azoverbindung, /. hydroxyazo compound, -benzol, n, hydroxybenzene (phenol), -bem-steinsaure. /, hydroxysuccinic acid (malic acid). -biazol, n. oxadiazole, oxdiazole. -bitumen, n, oxidized bitumen, -carbon-s ure, /, hydroxycarboxylic acid, -chlnoltn, n. hydroxyquinoline, -clunon, n. hydroxy-quinone. -chlorid, n. oxychloride, -chlor-kupfer, n. copper oxychloride, -cyan, n. oxycyanogen. 

Hydrazinotriazine 749 was prepared by the condensation of the respective quinone with thiosemicarbazide followed by sequential cyclization, chlorination with phosphorus oxychloride, and reaction with hydrazine (88JHC1139). Cyclocondensation of 749 with formic acid or carbon disulfide gave triazolotriazines 750 (88JHC1139) (Scheme 156). 

Carbon dioxide, clathrate in hydro-quinone, 7, 11 as a "hilfsgas, 18 hydrate, 3... 

Figure 3. Schematic representation of the common functional groups that are present on carbon (a) quinone (b) phenol (c) carboxyl (d) carbonyl (e) lactone (f) hydrogen.

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